Dosimetry In External Radiotherapy Research Articles

Review of real time 2D dosimetry in external radiotherapy: Advancements and techniques

The objective of this paper is to provide a comprehensive review of the advancements and techniques in real time two-dimensional (2D) dosimetry for external radiation therapy with emphasis in vivo dosimetry and patient specific quality assurance. External radiation therapy plays a crucial role in cancer treatment, delivering high-energy radiation beams to target tumours while minimizing damage to surrounding healthy tissues. Accurate dosimetry, as both the measurement of the dose and its delivered location, is paramount to ensure effective treatment outcomes and minimize potential side effects.The planned content of this paper encompasses a thorough examination of the advancements made in 2D dosimetry techniques, including solid state and electronic systems. The evolution from traditional passive dosimetry to modern real time detectors, such as portal imaging, has revolutionized the field, offering enhanced precision, efficiency, and convenience. This review will discuss the principles, advantages, and limitations of these systems, along with their practical implementation and calibration procedures.Furthermore, the paper will highlight novel technologies, such as luminescence coatings, for quality assurance (QA) and real-time dose verification during treatment. The use of innovative materials and designs in dosemeters, including high spatial resolution detectors and tissue-equivalent phantoms, will also be explored. Additionally, the incorporation of advanced data analysis techniques, such as machine/deep learning algorithms, for dose reconstruction and QA will be addressed.The review will also explore the application of real time 2D dosimetry in modern clinical and pre-clinical modalities, including intensity-modulated radiation therapy and volumetric modulated arc therapy, stereotactic radiosurgery, image-guided radiation therapy, particle therapy, adaptive radiotherapy, electron and proton ultra-high dose rate therapy and very high energy electrons.By providing an up-to-date overview of the state-of-the-art in real time 2D dosimetry in vivo dosimetry and patient specific quality assurance, this paper aims to inform and guide professionals in the field, facilitating the adoption of cutting-edge techniques and improving the accuracy and safety of external radiotherapy treatments.

8 ASN-IRSN Survey on in vivo dosimetry in external radiotherapy: what solutions and strategies to push the frontier of ”technically measurable”?

Introduction In Vivo Dosimetry (IVD) is mandatory in France for every ”technically measurable” beam, since 2008 (criterion No. 15 of National Cancer Institute, for the practice of external radiotherapy). IVD was historically based on punctual measurement techniques adapted to conventional radiotherapy. The applicability of this method has greatly decreased with the dissemination of modulated radiotherapy techniques (IMRT, VMAT). The majority of French radiotherapy centers practice these advanced techniques (nearly 70% of them in 2013 [1] ), for sometimes 100% of the treatments. So, the proportion of ”non-technically measurable” beams grows very rapidly and new solutions must be considered to ensure a satisfactory level of treatments control. From this statement, resulting from the practices observed during inspections, Nuclear Safety Authority (ASN) wished to know what IVD solutions - especially those called ”transit” based on the use of the portal imaging device (EPID) – are available or in development, the technical and organizational constraints of the ”transit” IVD and its relations with other types of controls. Methods IRSN met providers of IVD solutions, or comparable control systems, and visited radiotherapy departments experienced in the field of transit IVD. The Medical Physicists representatives (SFPM) point of view has been collected, in continuation with the SFPM work of 2014 [2] . Results This study focused on main ”transit” IVD solutions currently proposed and nearly expected, as well as alternative or complementary solutions such as the analysis and monitoring of the LINAC parameters. Interviews with medical physicists revealed that IVD is part of an overall process of dose verification and cannot replace the controls performed without the patient. The definition of the intervention criteria or validation of DIV results, the identification of dose gap origin of and the interpretation of the results are the main mentioned difficulties, as well as the ergonomics of the devices, the tools of monitoring and analysis, the accessibility of data and the need for consistent human resources. The teams’ expectations with respect to IVD, and therefore the requirements and resources allocated, can be on one hand a simple wish of regulatory compliance or, on the other hand, to use IVD as an adaptive radiotherapy tool . . Conclusions The offer of IVD solutions in recent radiotherapy techniques is progressing. The EPID-based IVD is the most widely used but, routinely, is often confined to conventional techniques. The exploitation and interpretability of the results is the main difficulty encountered by the teams, leading them to develop a treatment verification strategy in which the IVD is a one part of dose control and not the ultimate and global solution.

Which impact of tumor density variations on absorbed dose in external radiotherapy

Introduction Dosimetry in external radiotherapy is based on tomodensitometry images that are required to be previously calibrated and assume that the electron density is comparable to the mass density. In Magnetic Resonance Imaging, and in particular diffusion sequence, significant heterogeneities have been shown. These heterogeneities result in density variations within the tumor, e.g. glioblastomas. Purpose The aim of this study is to evaluate slight influence of mass density variations within the tumor via a dosimetric study. This can then be used to quantify the impact of those variations on modifications of dose 3D distribution. Materials and methods This study is devoted to dosimetric calculations realization using TPS Eclipse AAA used in clinical. Treatments were carried out with 5 X-ray beams of 6 MeV, in optimized dynamic Intensity-Modulated-Radiotherapy. Mass density changes of GTV for the same treatment plans have been tested from 1.04 (default tumor density) to 1.8 g.cm−3 in steps of 0.1. Results Dose-volume-histograms and profiles studies show a slight dose increase in surface GTV for the highest densities with significant changes isodose curves. Conversely, upon leaving the GTV, an under dosage of the tumor has been observed from a density variation from 1.04 to 1.2 g cm−3. It was noted that density differences of 0.5 and 0.8 g cm−3 caused failure to respect the prescribed dose limits of ± 3% in brain volumes of 1.5 and 25 cm3, respectively. Conclusion Dose distributions variations were recorded by densities changes. From a change of 0.5 g/cm3 within the tumor, dose prescriptions limits are not any more guarantees.

Cost-effect and ethical reasoning in radionuclide therapy dosimetry under the new EU BSS

Introduction Radionuclide therapy (RT) dosimetry is wide-ranging, sometimes complex, and always needs resource allocation. From Iodine-131 (e.g. hyperthyroidism) to Lutetium-177 (e.g. neuroendocrine cancers) or Itrium-90 (e.g. radioembolization), there is a broad range of radionuclides and activities for therapeutic use. Since each patient is unique, a personalized dosimetry approach can therefore be recommended. Purpose New developments in the field, and the new EU BSS Directive, are approaching dosimetry in RT to dosimetry in External Radiotherapy. However, there is a price to attain this goal and it needs to be justified. Materials and methods Beauchamp and Childress beneficence principle is evoked to justify dosimetry in almost every patient subjected to RT, although the cost of such procedures can be onerous for the majority of the already overloaded health care systems. This fact, together with necessarily limited available funding, can conflict with the principle of justice, stated by these authors, when allocating resources, leading to the need of rationing and ethical reasoning. Results Dosimetry implementation according to the EU BSS Directive must be carefully considered for each particular patient and pathology. The same Directive also strongly reinforces the medical physics expert (MPE) as part of the therapeutic team for RT. This implies that MPE are fundamental elements in the process of decision whether dosimetry should or not be performed in each particular circumstance. Conclusion MPE should be aware of the vast range of ethical values and reasoning behind clinical decision making, and a formal education in Bioethics should be pursued by these professionals. Disclosure The author has no relevant financial or nonfinancial relationships to disclose.

Development of Dose Verification Method for In vivo Dosimetry in External Radiotherapy

The purpose of this study is to evaluate the developed dose verification program for in vivo dosimetry based on transit dose in radiotherapy. Five intensity modulated radiotherapy (IMRT) plans of lung cancer patients were used in the irradiation of a homogeneous solid water phantom and anthropomorphic phantom. Transit dose distribution was measured using electronic portal imaging device (EPID) and used for the calculation of in vivo dose in patient. The average passing rate compared with treatment planning system based on a gamma index with a 3% dose and a 3 mm distance-to-dose agreement tolerance limit was 95% for the in vivo dose with the homogeneous phantom, but was reduced to 81.8% for the in vivo dose with the anthropomorphic phantom. This feasibility study suggested that transit dose-based in vivo dosimetry can provide information about the actual dose delivery to patients in the treatment room.

Quality assurance in radiation oncology. A study of feasibility and impact on action levels of an in vivo dosimetry program during breast cancer irradiation

Background and purpose: The study was aimed at investigating the feasibility and accuracy of an in vivo quality assurance program in radiotherapy. Breast irradiation was found to be a relevant clinical model due to the fairly good uniformity of the irradiated tissue. Materials and methods: The investigation was based on an extension of the method described by Leunens et al. (Leunens, G., van Dam, J., Dutreix, A. and van der Schueren, E. Quality assurance in radiotherapy by in vivo dosimetry. 1. Entrance dose measurements, a reliable procedure. Radiother. Oncol. 17: 141–151, 1990; Leunens, G., van Dam, J., Dutreix, A. and van der Schueren, E. Quality assurance in radiotherapy by in vivo dosimetry. 2. Determination of the target absorbed dose. Radiother. Oncol. 19: 73–87, 1990; van Dam, J. and Marinello, G. Methods for in vivo dosimetry in external radiotherapy. Physics for clinical radiotherapy. ESTRO Booklet n. 1 (Garant), 1994), determining the absorbed dose at any point on the central axis from a measurement of entrance and exit doses with individually calibrated and corrected diodes. Treatment accuracy ( Δ) was quantified as the ratio of the measured and the expected isocentre dose from the treatment planning system (TPS). Results: A preliminary study was carried out on a Plexiglas slab phantom to test the method ending with a frequency distribution of Δ with a mean of 0.04±0.05% and a standard deviation (SD) of 0.83±0.04%. In the in vivo study, 101 patients irradiated with two tangential fields were included in the protocol over a 1-year period. The total number of patient set-ups analyzed was 421 giving a distribution of Δ with a mean of −1.3±0.2% and an SD of 2.7±0.1% without any correction. Taking into account temperature effects and set-up errors as SSD accuracy and diodes positioning it was possible to implement an off-line correction method leading to a final distribution with a mean of −1.9±0.2% and an SD of 2.4±0.1%. Individual cases with large deviations were detected and evaluated and actions were undertaken whenever possible. Conclusions: The study showed that diodes can be easily used by radiographers in an accurate in vivo quality assurance (QA) program and that an accuracy level of 3% at 1 SD can be reached on average. Attention and action levels can also be identified and careful evaluation of positioning and morphological variations during treatment should be part of a comprehensive QA program.